1. Field of the Invention
This invention relates to a magnetic recording disk cartridge, and more particularly to a magnetic recording disk cartridge for a magnetic recording disk which is small in diameter and extremely thin in thickness and which is rotated at a high speed for recording or reproduction.
2. Description of the Prior Art
There has come into wide use as a recording medium for an electronic computer a floppy disk which is a flexible disk of polyester resin coated with magnetic material on the both sides thereof and on which digital information is recorded by a magnetic head. The floppy disk is easy to handle and inexpensive.
Recently, there has been proposed a photographic still camera in which, instead of a conventional silver salt photographic film which cannot be reused, a magnetic recording disk smaller than the floppy disk both in thickness and diameter is used as a recording medium. This still camera is generally referred to as "an electronic camera". This electronic camera is generally as large as a typical 35 mm photographic camera. In the electronic camera the image of an object is magnetically recorded on the magnetic recording disk while the disk is rotated at a high speed. Generally the magnetic recording disk for the electronic camera is accommodated in a hard casing to form a cartridge and is loaded in the camera body together with the casing.
Though in the conventional floppy disk, the disk is provided with an engaging hole at its center to be supported on its both side, the recording disk for the electronic camera is provided with a hub at its center, the hub being adapted to be engaged with a rotational shaft inserted into the cartridge from one side thereof.
In recording images using a magnetic recording medium, signals recorded on the magnetic recording medium at high density since video signals have a wider frequency band than digital signals or audio signals. Accordingly, when fine unevenness, scratches or flaking exists in the magnetic coating on the magnetic recording medium or when dust is deposited on the magnetic coating, so-called drop-out occurs during reproduction and the recorded signals cannot be faithfully reproduced. Since the magnetic recording disk cartridge for the electronic camera is frequently used outside, it is normally subjected to vibrations while carried and the surface of the magnetic coating on the recording disk is apt to be brought into contact with the inner surface of the hard casing and scratched thereby. Further, dust is apt to get into the inside of the casing through a magnetic head receiving opening formed in the casing through which a magnetic head has access to the recording disk for recording or reproduction.